Stabilized isoolefin polyolefin interpolymer derivatives and method of producing same



Patented June 22, 1954 UNITED STATE TNT OFFICE STABILIZED ISOOLEFINPOLYOLEFIN INTERPOLYMER DERIVATIVES AND METHOD OF PRODUCING SAME NoDrawing. Application September 5, 1952, Serial No. 308,167

Claims. (Cl. 260-457) The present invention relates to the stabilizationof isoolefin polyolefin interpolymer derivatives and, in particular, tocompositions comprising a rubbery brominated or bromine-containinginterpolymer of an isoolefin hydrocarbon and a polyolefin hydrocarbon,together with a metal silicate stabilizer therefor, and to methods ofproducing such compositions.

Among the known synthetic rubbers are the solid plastic interpolymers ofa major proportion of an isoolefin such as isobutylene and a minorproportion of one or more polyolefins (that is, diolefins, triolefins orother olefins containing more than one double bond), which interpolymersare characterized by high molecular weight, low unsaturation andreactivity (vulcanization or curing) with sulfur to yield an elasticproduct. Such interpolymers are described in U. S. patents includingNos. 2,322,073; 2,356,128; 2,356,129; 2,356,130; 2,373,705; 2,384,975;2,418,912 and 2,568,656 and in copending application Serial No. 166,979filed June 6, 1950. The presently best known examples of suchinterpolymers are the copolymers of isobutylene with a small proportionof isoprene or butadiene known to the rubber industry as Butyl (orG-R-I) rubber.

While Butyl rubber has found considerable use in the manufacture ofinner tubes, it possesses inherent disadvantages which have preventedits more widespread use. It vulcanizes or cures more slowly than otherwidely used sulfur-vulcanizable rubbery materials; it does not adherewell to other materials including natural rubber, and when it is mixedwith natural rubber and the mixture vulcanized the resultingvulcanizates are generally less valuable than vulcanizates from eitherof the rubbery materials alone.

It is disclosed in our copending application Serial No. 156,724 filedApril 18, 1950, of which this application is a continuation-in-part,that the introduction of bromine atoms into the polymer structure ofButyl rubber and similar isoolefin-polyolefin interpolymers, so as toproduce units of the structure Bl' Bl' as by bromination of suchinterpolymers, results in the obtainment of new materials withproperties unexpectedly superior to those of the bromine-free materials.Such brominated rubbery isoolefin-polyolefin interpolymers cure orvulcanize quite rapidly, even with vulcanizing agents which are totallyineffective with the unbrominated materials, to yield vulcanizedproducts 'vulcanizates from unbrominated which far surpass thoseobtained from the unbrominated materials in a number of respectsincluding a much greater ability to withstand the sheets of heat andaging, and a lower permanent set, and which are fully equal or superiorto the materials in other respects such as tensile strength andelasticity, low temperature flexibility and resistance to air-diffusion.In addition, the brominated interpolymers, unlike the unbrominatedmaterials, adhere well to a wide variety of materials including metals,plastics, and natural and. synthetic rubbers and are, therefore, ofconsiderable value as adhesives; they may also be mixed with naturalrubber or any of the various known butadiene synthetic rubbers in anydesired proportions and the resulting mixtures co-vulcanized to giveproducts of excellent properties.

It has been found, however, that the rubbery brominated isoolefinpolyolefin interpolymers are per se somewhat unstable as evidenced bytheir development of color upon heat aging or upon long standing at roomtemperature and by their becoming progressively tougher during storageor heat aging or during the Mooney viscosity determination. Their lackof stability also sometimes results in progressive degradation of theirvulcanizates, during extended exposure to heat, in such physical andchemical properties as tensile strength, elongation, modulus, flex-life,ozone resistance, and adhesiveness.

The invention of this application resides in the discovery that suchbrominated isoolefin polyolefin interpolymers may be eificientlystabilized against such undesirable changes by incorporating therein asmall amount of a metal silicate of a class to be hereinafter defined.The resulting stabilized composition is possessed of the properties ofthe original brominated interpolymer and in addition is suiiicientlystable to withstand prolonged storage and exposure to heat and light andother deleterious influences. Vulcanizates prepared from thesilicate-containing compositions are likewise of superior stability toheat and possess improved physical properties especially at hottemperatures.

The metal silicate stabilizers of this invention are the silicates ofmetals occurring in group II of the periodic table. Calcium silicate isgreatly preferred although other alkaline earth metal silicates such asbarium and strontium silicate, as well as the silicates of magnesium,zinc, cadmium and other group II metals may also be used.

The silicate stabilizers used in this invention a may benaturally-occurring or they may be synthetically prepared byprecipitation or fusion. It is preferred to precipitate the silicate inas finely-divided a state as is possible and to grind the fused silicateto a fine state of sub-division before use. The particle size should bepreferably that of the commonly used pigments, fillers, stabilizers,etc. in common use in the rubber industry.

The silicate stabilizer may be incorporated into the brominatedinterpolymer at any time before vulcanization although it is preferredto incorporate the stabilizer as an integral step in manufacture of thebrominated interpolymer. If incorporated into the solid brominatedinterpolymer, this may be done satisfactorily on a tworoll rubber millor in a Banbury-type or other internal mixer or by dissolving ordispersing the brominated interpolymer in an appropriate medium andadding a silicate dispersion or suspension thereto. The preferred methodis to blend a stabilizer dispersion or suspension with a solutioncontaining the brominated intcrpolymer as obtained from the brominationprocess and effect coprecipitation of the brominated interpolymer andthe silicate stabilizer in the form of discrete particles in which thelatter is uniformly dispersed in the former. The exact manner in whichthe preferred incorporation step is carried out will be more fullydescribed in the description below.

The amount of the silicate stabilizer required for eificientstabilization will vary somewhat depending on the interpolymer treatedand on its bromine-content, on the silicate utilized and on its finenessand compatibility with the rubber. In general, significant stabilizationis noted, especially with calcium silicate, in amounts as little as 1%by weight based on the rubbery interpolymer. The beneficial effectincreases with in creasing amounts of silicate stabilizer up to about 5to Beyond 10% the additional silicate seems to function only as afiller, although beneficial in most cases. For stabilization only,however, amounts of l or 2 to 5% are preferred. For combined stabilizerand filler action (as in white sidewall tire compounds utilizing calciumsilicate) amounts up to to volumes or more of silicate per 100 volumesof bromine-containing interpolymer or from 1 to 100% by weight or moremay be utilized.

The brominated isoolefin-polyolefin interpolymers in which thestabilizer is incorporated are prepared, according to the preferredprocedure of our copending application Serial No. 156,724, now U. S.Patent 2,631,984, by reacting a rubbery isoolefin-polyolefin hydrocarboninterpolymer with a brominating agent, preferably in solution. Since thereaction which occurs involves an addition of bromine to olefinic doublebonds, the isoolefin-polyolefin interpolymer used must and will, ofcourse, contain olefinic unsaturation, but its nature may otherwise bevaried widely.

Preferred isoolefin-polyolefin interpolymers for use in preparingbrominated derivatives are the solid, plastic rubbery interpolymers (inother words, high molecular weight polymers) of a major proportion, moredesirably from 70 to 99% by weight, of an isoolefin generally containingfrom 4 to 8 carbon atoms and a terminal methylene group, such as, mostdesirably, isobutylene or, alternatively, 3-methyl butene-l, 4-methylpentene-l, 2-ethyl butene-l, ll-ethyl pentene-l, 4-ethyl hexene-l or thelike, or a mixture of such isoolefins, with a minor proportion,desirably from 1 to 30% by weight of a polyolefinic hydrocarbongenerally containing from 4 to 13 carbon atoms, or two, three or moresuch polyolefinic hydrocarbons, including the following:

(1) acyclic diolefins or open-chain, aliphatic conjugated dienes such asbutadiene-1,3 isoprene, 2,4-dimethyl butadiene-1,3, piperylene, 3-methyl pentadiene-1,3, hexadiene-2A, 2-neopentylbutadiene-1,3 and thelike;

(2) acyclic non-conjugated diolefins such as dimethallyl and itshomologs containing 2 to 6 carbon atoms interposed between twoisopropenyl radicals, 2 methyl heXadiene-LS, Z-methyl pentadiene 1,4, 2methyl heptadiene 1,6, 2- methyl heptadiene-L i and other tertiarynonconjugated diolefins having one double bond in the terminal positionattached to a tertiary carbon atom;

(3) alicyclic diolefins, both conjugated and non-conjugated, such ascyclopentadiene, cyclohexadiene, l-vinyl cyclohexene-B, l-viriylcyclohexene-l, l-vinyl cyclopentene-l, l-vinyl cyclobutene-2,dicyclopentadiene, and the like as well as monocyclic diolefinicterpenes such as dipentene, terpinenes, terpinolene, phellandrenes,sylvestrene and the like;

(4) acyclic triolefins such as 2,6-dimethyl-4- methylene-heptadiene-2,5,Z-methyl hexatriene- 1,3,5 and other conjugated triolefins, as well asmyrcene, ocimene, allo-ocimene and the like;

(5) alicyclic triolefins such as fulvene, 6,6- dimethyl fulvene,6,6-methyl-ethyl fulvene, 6- ethyl fulvene, 6,6-diphenyl fulvene,G-phenyl fulvene and other fulvenes of the formula HC-CH 2 3 where R ishydrogen, alkyl, cycloalkyl, or aryl; as well as other alicyclictriolefins such as 1,3,3- trimethyl-B-vinyl cyclohexadiene-ZA,cycloheptatriene, etc.;

(6) higher polyolefins such as 6,6-vinyl methyl fulvene (a tetraolefin)and 6,6-diisopropenyl fulvene (a pentaolefin), and

(7) aromatic hydrocarbons containing a plurality of olefinica-llyunsaturated non-aromatic hydrocarbon groups such as vinyl groups,representative of which are divinyl benzene and similar polyvinyl orpolyisopropenyl aromatic hydr carbons.

Such solid, plastic, rubbery interpolymers, for use in preparingbrominated derivatives, are themselves generally prepared by lowtemperature polymerization (from 0 to C.) utilizing an appropriatecatalyst, generally an active metal halide or Friedel-Crafts typecatalyst such as aluminum chloride or boron trifluoride, dissolved in alow freezing solvent such as methyl or ethyl chloride, and, when soprepared, generally possess an average molecular weight above 15,000 andoften as high as 30,000 to 120,000 or higher, iodine numbers in therange 0.5 to 50, and are reactive with sulfur to yield elastic products.Most important of these are the solid plastic interpolymers ofisobutylene with small amounts of isoprene or butadiene, of the typeshown as Butyl or GRI rubber.

However, it is to be understood that the silicate stabilizers areequally effective when applied to brominated interpolymers made fromisoolefin polyoleiin interpolymers other than the preferred materialsset forth above. Any of the known isooleiin-polyolefin hydrocarboninterpolymers may be converted to useful brominated derivatives andutilized in the method of this invention. For example, resinousinterpolymers of low molecular weight and/or not readily vulcanizablewith sulfur are readily converted to brominated derivatives havingenhanced adhesive properties and the ability to be utilizedadvantageously in the compounding of rubbery materials. Similarly,isoolefin-polyolefin hydrocarbon interpolymers containing otherinterpolymerized monomers such as styrene, chlorostyrenes, acrylylchloride, methallyl chloride, and other monoolefinic monomers also areadvantageously utilized to prepare brominated derivatives. Toillustrate, a brominated interpolymer of 50% isobutylene, 30% styreneand 20% isoprene is superior to the corresponding unbrominatedinterpolymer as an adhesive and in the compounding of rubbery materials.

In preparing the brominated derivatives for use in this invention, anybrominating agent may be utilized such as molecular bromine itself orthe compounds of bromine which liberate molecular bromine among whichare sodium hypobromite, magnesium bromide hexahydrate,N-bromo-succinimide, alpha-bromoacetoacetanilide, betabromoethylphthalimide, [N-bromoaoetamide, tribromo phenol bromide,bromo-beta-naphthol, pyridinium bromide perbromide, etc.

In accordance with the disclosure of our copending application SerialNo. 156,724 the bromination may be carried out in many ways. One

method consists in preparing a solution, dispersion or cement of theinterpolymer in an appropriate normally liquid organic solvent ordiluent such as a hydrocarbon or halogenated derivative thereof(examples of which are toluene, chlorobenzene, hexane, heptane,trichloroethane, carbon tetrachloride, etc.) and adding the brominatingagent either as such or in solution, for example, in carbontetrachloride, to the resulting in terpolymer solution, dispersion orcement thereby to form the brominated interpolymer in solution ordispersion in the solvent or diluent. The resulting solution ordispersion may be utilized as such, as, for example, when the brominatedderivative is employed as an adhesive, or it may be admixed with anon-solvent for the brominated derivative (such as alcohol or water) toprecipitate the brominated derivative which is then recovered in thesolid, finely-divided or crumb-like form, in either of which cases it ispreferred that the silicate stabilizer be incorporated in the solutionor dispersion of brominated interpolymer before utilizing the latter asan adhesive or before precipitation thereof.

A more preferred method, particularly advantageous to those having Butyltype polymerization equipment consists in utilizing as the solvent ordiluent for the bromination a saturated hydrocarbon or halogenatedderivative thereof which boils below room temperature such as methyl orethyl chloride or butane, and carrying out the bromination at atemperature and pressure such that the solvent is maintained in theliquid state. This greatly simplifies recovery of the solvent or diluentsince the resulting solution of brominated interpolymer can be run intowater above the boiling point of the solvent or diluent so that thelatter is flashed oil and condensed while the brominated interpolymer isprecipitated or coagulated in a conveniently handled crumb-like form.The ethyl chloride solution of interpolymer utilized in this variationof the process is conveniently prepared by dissolving the solidinterpolymer in the solvent. Preferably, the

ethyl chloride solution resulting from the Butyl I type polymerizationmay be utilized directly with addition thereto of a soluton of brominein ethyl chloride or carbon tetrachloride followed by quenching with analkaline material which results both in neutralization of excess bromineand inactivation of the Friedel-Crafts catalyst.

Another method of preparing brominated interpolymers consists in passingbromine vapors over a finely-divided or shredded solid interpolymer.Still another method, also applicable to solid interpolymers, resides inadding a solid brominating agent to the interpolymer on a mixingmill,followed by heating the mixture to a tem perature above that at whichthe brominating agent decomposes to liberate molecular bromine.

Regardless of the particular method employed for eifecting thebromination, it has been found that the bromination reaction occursquite rapidly and essentially involves the addition of bromine to theolefinic double bonds of the interpolymer. Consequently, the resultingbrominecontaining interpolymers possess in their structure units of theformula Br Br These units not found in known isoolefin-polyolefinhydrocarbon interpolymers, may well be responsible, at least in part,for the unique properties of the bromine-containing interpolymers.

It should be pointed out, however, that some substitution may andprobably does occur, along with addition of bromine to olefinic doublebonds, during the bromination reaction, and that, therefore, it is notessential that all combined bromine be present in the structure.

However, it has been found that if the bromination is carried out attemperatures at or above room temperature or if the contact betweenexcess bromine and the interpolymer is prolonged, a marked degradationof the physical properties of the product may occur. This degradationmanifests itself as a pronounced softening or reduction in apparentmolecular weight. It is not fully understood but it is believed thatmolecular bromine may be an active depolymerization agent or thatsubstituted bromine as distinguished from bromine added to olefinicbonds, may favor depolymerization. Regardless of the cause, most usefulbrominated inter-polymers are produced when substitution and exposure tomolecular bromine is kept at a minimum. Such a reaction is efiicientiycarried out in a pipe line or other elongated positive through-put typeof reactor in a continuous manner. Since the addition reaction appearsto be almost instantaneous, the prompt addition of an alkalineneutralizer such as potassium hydroxide or sodium carbonate shortlyafter initial mixing of the rubber and bromine solutions also favorsproduction of most useful brominated interpolymers.

The amount of bromine which combines with the interpolymer duringbromination depends upon the brominating agent being used, the method ofbromination and the concentration of aeals e brominating agent. Whenother factors are constant under the preferred conditions of lowtemperature and short contact time there appears to be an approximatestraight line relationship between the original concentration ofavailable bromine and the amount of bromine combined with theinterpolymer. of combined bromine is about to that of the originalconcentration of bromine while under accurately controlled conditions itis usually about A. This is quite advantageous since the bromine contentof the product can be controlled rather closely simply by regulating theoriginal concentration of the brominating agent.

The brominated interpolymers resulting from the bromination reaction maycontain from as little as 0.5% by weight or to 4, 8, or even by weight,or even as much as 50% by weight of combined bromine depending on thedegree of unsaturation of the parent interpolymer, which in turn dependsupon the proportion of combined polyolefin in the interpolymer utilized.Preferably, for any given derivative, the percentage of combined bromineis less than that which would theoretically be present if all theolefinic C:C units) double bonds were completely brominated to giveunits, and preferably, for high molecular weight rubberyisoolefin-polyolefin interpolymers having an iodine number less than 50,that is of the nature of Butyl rubber, the percentage of combinedbromine is from to 80% of the possible theoretical amount. Still morepreferably, the percentage of combined bromine in such interpolymers isin the range of 1 to 8% by weight, and for adhesive applications is inthe range of 1.5 to 4% by weight. Most useful brominated interpolymersare those derived from Butyl rubber in which the percentage of combinedbromine is to of theoretical or 2.5 to 4.5% by weight or, moreparticularly, about 3 by weight.

From the foregoing, it is apparent that the preferred brominatedinterpolymer derivatives for use in this invention are not completelysaturated but that they are less unsaturated than the parentunbrominated interpolymers. Their molecular weights are not preciselyknown but they are of the same order as the parent interpolymer. Eventhough some depolymerization may occur during bromination their apparentmolecular weights are generally about the same or slightly higherbecause of the presence of the relatively heavy bromine atoms.

Bromination of isoolefin-polyolefin interpolymers so as to produce unitsis not the only method of arriving at interpolymers containing suchunits, but is at present preferred. Another method consists ininterpolymerizing an isoolefinic monomer with a polyolefinic monomer atleast one of which monomers is brominated so as to contain thestructure. For example, the interpolymerization In general, the amountof isobutylene with 2,3-dibromo-butadiene-1,3 (which has the results inthe production of an interpolymer containing such units; thisinterpolymer, however, is more unsaturated for a given bromine contentthan are the bromine-containing interpolymers produced by thebromination of isoolefin-diolefin interpolymers.

As mentioned above, the bromine-containing isoolefin-polyolefininterpolymers are possessed of unique properties in and of themselvesand when stabilized according to this invention, are exceedingly useful,especially in adhesives, in the manufacture of inner tubes, thetire-curing bags, etc. (where great heat stability, resistance to airdiffusion, oxygen, steam, water, ozone etc. are required) and forvarious other purposes of particular importance in manufacture of tiresand a multitude of other rubber products, in which the unbrominatedisoolefin-polyolefin interpolymers are not entirely satisfactory. Forexample, the stabilized brominated interpolymers of this invention,without further addition of compounding ingredients, are excellentadhesives to bond rubbery materials to each other or to metal and otherstructural materials, being especially useful in bonding theunbrominated isoolefin-polyolefin interpolymers to each other, tonatural rubber and to diene synthetic rubbers. The stabilizedbromine-containing interpolymers are compatible in all proportions withthe natural and diene synthetic rubbers forming vulcanizable admixturestherewith which possess the desirable properties of remarkably increasedozone resistance, improved resistance to flexing, and increasedresistance to air diffusion. In any of these uses they may be compoundedwith any of the conventional ingredients used in compounding theunbrominated rubbery isoolefin-polyolefin interpolymers or other rubberymaterials, and they maybe vulcanized by the same general methods. Theirvulcanization proceeds much. more rapidly than that of the unbrominatedmaterials, despite their generally lower degree of unsaturation, andthey may be vulcanized in the absence of sulfur with agents, such as thepolyvalent metal oxides particularly zinc oxide, which are ineffectivein vulcanizing the parent unbrominated interpolymer.

The preparation of representative brominecontaining interpolymers andtheir stabilization according to this invention are more fully set forthin the following examples which are illustrative only since numerousvariations and modifications therein will be apparent to those skilledin the art. In the examples, all parts, unless otherwise indicated, areby weight.

EXAMPLE 1 91 parts of a solid plastic rubbery copolymer of about 97%isobutylene and 3 isoprene known as Butyl or GEL-15 is dissolved insufficient eheptan to o a fl i pn- 9 part of liquid bromine as a 10%solution in carbon tetrachloride are then added to the heptane solutionand the resultin mixtures rc for bout 1 9s? in the dark. An excess ofsodium carbonate as a to 30% solution in water is then added toneutralize the unreacted bromine. After a short period of agitation theneutralized brominated cement is blended with a quantity of methanol toprecipitate the brominated copolymer, the latter then being filtered,washed and dried. The brominated copolymer thus obtained contains 2.25%of combined bromine and is slightly softer than the parent copolymer.

The copolymer when vulcanized by sulfur either alone or in blends withnatural rubber or with butadiene styrene or butadiene-acrylonitrilesynthetic rubber forms strong, highly useful compositions. However, whenthe raw brominated copolymer is allowed to stand in air at 70 C. itbecomes tough, in fact in 3 days it becomes so tough as to be somewhatdifficult to process. This toughening, without substantial change inbromine content, is illustrated by the following data for the rawbrominated copolymer, after aging, as to its bromine content and Mooneyviscosity at 1 minute, 10 minutes, and 20 minutes using the 1.2 inchrotor at 250 R:

The physical properties of vulcanizates of the brominated copolymer alsodeteriorate during aging at 70 C., the tensile strength of a sulfurvulcanizate of an unaged sample of brominated copolymer in a 60/40 blendwith natural rubber being 1775 lbs./ sq. in. while that of a similarblend containing a brominated copolymer aged 3 days at 70 C. isconsiderably less.

The unstabilized brc'mi'nated cc oiymer also increases in Mooneyviscosity during a Mooney viscosity determination. After an initialreading of 21 a stock containing such copolymer evidences a Mooneyviscosity of 37 after 1 minute and 4'? after minutes at 250 F. When agedfor seven days at 70 C. the same stock is of a dark color and evidencesan initial Mooney reading of 51, a 1 minute Mooney of 76 and a 15 minuteMooney of 72.5. By contrast when only 1.25 on the brominated copolymerof a finely-divided precipitated calcium silicate known as Silene EF ismilled into the brominated copclymer the resulting composition is lightin color, has a 1 minute Mooney of 40 and a 15 minute Mooney of 22.After aging for seven days at 70 C. the stock is a very light brown incolor. Thus only 1.25% of calcium silicate is sufficient to stabilizethe brominated copolyiner during processing and to prevent blackening ofthe stock. When 2.5% of the same calcium silicate is incorporated theinitial Mooney reading is 19, the 1 minute Mooney is 38 and the 15minute Mooney is only 20.5. After aging '7 days at .Z0 C. the initialreading on this same composition is 39, the 1 minute Mooney is 42 andthe 15 minute Mooney is only at. Thus the use of 2.5% calcium silicatestabilizes the brominated copolymer not only during processing but alsoduring an accelerated 7 day heat aging.

The incorporation of calcium silicate into the brominatediscolefin-polyolefin interpolymer not only stabilizes the latter againstheat-induced changes in plasticity and color during processing 10 andstorage but also has a very beneficial efiect on the physical propertiesof vulcanized compositions prepared therefrom. Separate samples of theunstabilized brominated copolymer described above, both aged and unaged,and an aged sample of the stabilized composition containing 2.5% calciumsilicate are compounded with natural rubber and the usual sulfurvulcanization ingredients to form a white side wall tire compound Whenportions of each composition are vulcanized at 280 F. for varyingperiods of time the physical properties of the vulcanizates are as shownin the following Table I:

Table I Cure Unaged Min/280 F.

A ed7 da 5 Unstabilized g y Aged7 days 0. Unstabilized 5 Inspection ofthe data in Table I clearly shows that without stabilizer aging for '7days in air at 70 C. results in a lowering of the physical properties ofthe white side wall tire compound while with only 2.5% by weight ofcalcium silicate the physical properties are substantially unaffected.The composition containing calcium silicate also seems to have a fastercure rate than the aged unstabilized composition since optimum physicalproperties of the former are reached in 15 minutes while the lattershows signs of continued cure at 45 to '75 minutes. The aged calciumsilicate containing composition, moreover, was very white in color whilethe aged-unstabilized vulcanizate was a creamy buff. Similar results arenoted with amounts of calcium silicate ranging from 1 to 10% or more andwith equivalent amounts of barium silicate.

EXAMPLE 2 The isobutylene isoprene copolymer utilized in the brominationstep of Example 1 is dissolved in liquid ethyl chloride to form a 20%solution containing parts of copolymer. A solution containing 5 to 16parts of bromine dissolved in ethyl chloride is added to the copolymersolution at 0 C. in a closed vessel and the resulting mixture stirredfor five minutes at which point an excess of alcoholic potassiumhydroxide is added to neutralize the unreacted bromine. After stirringfor several minutes to allow neutralization to be completed an aqueousslurry of finelydivided calcium silicate (2.5 based on the weight ofbrominated copolymer) in water is added and the mixture stirred rapidly.Following further stirring to form a substantially homogeneous mixturethe contents of the reaction vessel are discharged in a fine stream orspray into a closed coagulating tank fitted with a condenser andcontaining hot water (6070 C.) and a colloidal dispersion of calciumsilicate, whereupon the ethyl chloride is flashed off and condensed andthe brominated copolymer is obtained as a fine crumb-like coagulumcontaining intimately dispersed calcium silicate. ihe presence ofcalcium silicate in the copolymer solution and in the coagulation bathassists in obtaining a fine, small sized and non-sticky crumb. Thecoagulum is finally separated by filtering and is washed once or twicewith clear water and dried.

The calcium silicate containing brominated isobutylene-isoprenecopolymer thus obtained contains from 1.5 to 6.0% of combined bromine(depending on the original amount of bromine used) and is a plastic,easily worked rubbery material having approximately the same Mooneyviscosity as the parent copolymer. Compounded with sulfur andaccelerators in the natural rubber white side wall tire compound ofExample 1 and then vulcanized, the copolymer derivative containing 2.5to 3.0% by weight of calcium silicate exhibits 2500 lbs/sq. in. tensilestrength and is white in color. After aging the copolymer derivative inair for as much as 28 days at 70 C. the color or physical properties ofits vulcanizates are substantially unchanged. When exposed to 27.9 p. p.h. m. of ozone at 280 F. while under 20% stretch the vulcanizaterequires 167 hours to show the first crack while a similar vulcanizateprepared without calcium silicate cracks in less than 100 hours.

EXAMPLE 3 A brominated isobutylene-isoprene copolymer of the type shownin Example 2 containing 3% combined bromine is compounded in a whiteside wall tire compound containing 40 parts of natural rubber (recipe ofExample 1) but in which a portion of the zinc oxide is omitted and anequivalent volume of calcium silicate and precipitated silicasubstituted therefor and 10 volumes respectively). The resultingcompound produces a vulcanizate having greatly superior tensile strengthand 400% modulus when measured at 212 F. The vuicanizate possessessuperior hot flexing properties and greatly superior ozone resistance.The flexing properties and ozone resistance of the stabilizedcompositions are particularly outstanding. The compositions containingcalcium silicate withstand approximately 1,000,000 fiexures in theDemattia apparatus while those not containing calcium silicate fail atabout 50,000 to 100,000 fiexures. when exposed under stretch to p. p. h.m. of ozone at 120 F. vulcanized compositions containing 1.5% and 4.5%calcium silicate do not show the first crack until at least 100 hoursexposure while the unstabilized vulcanizate cracks in hours.

Similar results are obtained, using from 1 to 10% or more of calcium,barium, or strontium, silicates, in blends of the above high molecularweight brominated copolymers with butadiene styrene copolymer rubbersand with butadiene acrylonitrile copolymer rubbers. Also, reclaimed orrefined butyl rubber after bromination is also efiiciently stabilized bythese metal'silicates and is highly useful in adhesive applications,particularly in adhering ordinary butyl rubber to natural and syntheticrubbers.

V EXAMPLE4 The brominated interpolymer of Example 2 Similarly containing3% combined or polymer-bound bromine and 2% of a polymeric plasticizersuch-as the polyester oil known as Paraplex G- is compounded with 4.5,15.0, 25.0 and 31.0 'parts per of polymer of the calcium silicatepigment known as Silene EF along with the other ingredients of the whiteside wall tire composition of Example 1. The vulcanizate resulting aftervulcanization for minutes at 280 F. along with that of a controlcomposition containing no calcium silicate are tested for their tensilestrength at 212 F. The control composition (which has a room temperaturetensile of 1650 lbs/sq. in. and an elongation of 705%) has at 212 F. atensile of only 233 lbs/sq. in. and an. elongation of only 415% whilethe compositions containing calcium silicate (which have roomtemperature tensile and elongation of 1600- to 1700 lbs/sq. in. and 600to 700%, respectively) show progressive improvement in hot tensile withincreasing cal- "cium silicate until the vulcanizate containing 31 partshas a 212 F. tensile of 640 lbs/sq. in. and a 212 F. elongation of 535%.

EXAMPLE 5 The previous examples have shown the effect of the silicatestabilizers on 60/40 blends of the brominate'd isoolefin-polyolefinpolymers with natural rubber. Blends with natural rubber ranging from 5to 95% of the bromine-containing polymer and 5 to 95% of natural rubberor natural rubber reclaim also are so stabilized. Similar stabilizationeiTects are noted also in vulcanizates prepared from thebromine-containing polymers alone and in blends with other natural andsynthetic rubbers and reclaimed forms of such rubbers. Specifically,blends ranging from 10 to 95% by weight of the bromine-containingisoolefin-polyolefin polymer and 5 to 95% of butadiene acrylonitrilecopolymer rubbers are similarly stabilized against discoloration in theraw polymer state and in the form of sulfur-vulcaniz'ates are stabilizedduring heat-aging and are possessed of better hot-flexing and hottensile properties. Also similar blends with butadiene styrene copolymerrubbers, polychloroprene rubbers, unbrominated Butyl rubbers,thiokol-type rubbers and other are also efliciently stabilized bycalcium silicate.

EXAMPLE 6 Other brominated isoolefin-polyolefin hydrocarboninterpolymers show a similar response to the incorporation of the metalsilicates of this as is shown in the foregoing examples. Still otherisoolefin-polyolefin hydrocarbon interpolymers easily converted tobrominated derivatives and stabilized by the metal silicates of thisinvention are interpolymers of isobutylene or another isoolefin withisoprene and/or 1 to 5% of cyclopentadiene, dicyclopentadicne,1-vinylcyclohexene-3, myrcene and others.

--From the foregoing description of the invention, it willbe seenthatthe stabilized brominecontainin interpolymer compositions constitutea new, greatly improved and widely useful class of materials. It isapparent, therefore, that various embodiments of the invention, inaddition to those specifically disclosed, may be provided withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

We claim:

1. The method of stabilizing an interpolymer of an isoolefinichydrocarbon containing 4 to 8 carbon atoms and a terminal methylenegroup and a polyolefinic hydrocarbon containing at least 0.5% by weightof combined bromine of addition which comprises incorporating therein asilicate of a metal occurrin in group II of the periodic table.

2. A rubbery composition comprising a brominated rubbery interpolymer ofan isoolefinic hydrocarbon containing 4 to 8 carbon atoms and a terminalmethylene group and. a polyolefinic hydrocarbon, said brominatedinterpolymer containing at least 0.5% by weight of combined bromine and,as a stabilizer therefor, a silicate of a metal occurring in group II ofthe periodic table.

3. A rubbery composition comprising a partially-brominated derivative ofa rubbery interpolymer of a major proportion of isobutylene and a minorproportion of a butadiene-1,3 hydrocarbon, said brominated derivativecontaining combined bromine ranging from 20 to 80% of that theoreticallyrequired to react with the double bonds of the original interpolymerand, as a stabilizer therefor, calcium silicate.

4. A rubbery composition comprising a partially-brominated derivative ofa rubbery interpolymer of from '70 to 90% by Weight of isobutylene andfrom 1 to by weight of isoprene, said brominated derivative containingcombined bromine ranging from 20 to of that theoretically required. toreact with the double bonds of the original interpolymer and, as astabilizer therefor, finely-divided calcium silicate.

5. A rubbery composition comprising a partially-brominated derivative ofa rubbery copolymer of isobutylene and isoprene containing from 2 to 4%by weight combined bromine and, as a stabilizer therefor, finely-dividedcalcium silicate.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,179,973 Alexander Nov. 14, 1939

1. THE METHOD OF STABILIZING AN INTERPOLYMER OF AN ISOOLEFINICHYDROCARBON CONTAINING 4 TO 8 CARBON ATOMS AND A TERMINAL METHYLENEGROUP AND A POLYOLEFINIC HYDROCARBON CONTAINING AT LEAST 0.5% BY WEIGHTOF COMBINED BROMINE OF ADDITION WHICH COMPRISES INCORPORATING THEREIN ASILICATE OF A METAL OCCURRING IN GROUP II OF THE PERIODIC TABLE.